Experiments with 3 activated sludge processes have been made. They were fed with 3 different types of wastewater: raw wastewater, centrifuged wastewater and raw wastewater with extra suspended solids added. All 3 processes were operated at identical loadings of 0.06 kg COD/kg VVS·d. The experiments demonstrated that the raw wastewater solids had considerable influence upon the oxygen and nitrate respiration rates observed in the activated sludge biomass. In the present case the oxygen respiration rates were reduced by the introduction of raw wastewater solids into the activated sludge process. The nitrate respiration rates, however, were increased by the raw wastewater solids. These effects could have influence upon the design of activated sludge processes for carbon and nitrogen removal, with respect to the use of primary settling.
